What is 'reverse block' in diving?

The term 'reverse block' in diving refers to a situation where gas expands in the body during ascent, causing an obstruction. This phenomenon typically occurs when gas trapped in air spaces, such as the sinuses, middle ear, or lungs, cannot equalize properly as a diver ascends. When divers ascend, the pressure around them decreases, causing any gas in the body to expand. If this expansion is not managed, it can lead to painful obstructions and even potential injury.

Understanding reverse block is vital for divers to recognize the importance of equalizing their air spaces throughout the dive, particularly during ascent, to avoid complications such as barotrauma. Proper techniques for equalization, such as the Valsalva maneuver, help to prevent this issue, ensuring a safe ascent process.